1. Field of the Invention
This invention relates to an improved process for the chloromethylation of aromatic material, especially vinyl aromatic resins, such resins being useful after subsequent reaction with amines and optionally further reaction with alkyl halides as weak base and strong base anion exchange resins.
2. Description of the Prior Art
Chloromethylation, as used herein, is the reaction of an aromatic polymeric material, e.g., polystyrene, usually crosslinked, and in gellular or porous form, with a reagent which causes the introduction of chloromethyl groups onto the aromatic ring. For many years, a preferred process has employed the reaction of externally or separately prepared chloromethyl methyl ether (optionally "CME" herein) with the polymer, which introduces the chloromethyl groups and produces methanol and other by-products and decomposition products of the CME. Excess chloromethyl methyl ether remaining after the chloromethylation reaction is complete is deactivated or "quenched" and the polymer usually then further reacted to form the desired anion or cation exchange resin. As used herein and in the appended claims "polymer(s)" is intended to include copolymers, particularly insoluble crosslinked copolymers. Products derived from such polymers, such as ion exchange resins, are usually called "resins".
Because the production of chloromethyl methyl ether is usually accompanied by the production of small amounts of the carcinogenic bis(chloromethyl) ether, it is highly desirable to lessen or eliminate the separate or external production of chloromethyl methyl ether and to recover and reutilize unreacted chloromethyl methyl ether from the reaction mixture, especially when excess chloromethyl methyl ether is used in the preparative reaction to increase the extent of chloromethylation and/or to serve as a swelling agent for the polymer to be chloromethylated (see U.S. Pat. No. 4,207,398, issued 6/10/80).
An "in situ" procedure as taught, inter alia, by Boutier et al., U.S. Pat. No. 4,225,677, is known for generation of chloromethyl methyl ether wherein chloromethylating complexes, such as from a mixture of methanol, formaldehyde, and chlorosulfonic acid, are formed in the presence of or with an immediate addition of resin and catalyst. Although such a procedure addresses certain of the toxicity and handling problems associated with external generation of chloromethyl methyl ether, difficulties are encountered in control of the chloromethylation reaction conditions, such as non-uniform reaction of the beads, and in removal of unwanted by-products, such as sulfuric acid. The present process, by cleanly separating the chloromethyl methyl ether generation/regeneration process from the chloromethylation reaction, avoids such process difficulties.
Pascu et al, Romanian Pat. No. 79140, teach addition to the chloromethylated polymer, after completion of the chloromethylation reaction, of concentrated hydrochloric acid and of formaldehyde under specified ratios based on the chloromethylated polymer present, followed by distillation of the resultant mixture to recover chloromethyl methyl ether. The distilled chloromethyl methyl ether is re-used in a second chloromethylation, but further chloromethyl methyl ether must be added to complete the second reaction.
Pashkov et al., British Pat. No. 1,162,078 teach treatment of the waste products remaining from the chloromethylation with methanol prior to distillation, for the purpose of regenerating methylal from the excess chloromethyl methyl ether present. New chloromethyl methyl ether must be generated for a second chloromethylation reaction.
Hauptmann et al, East German Unexamined patent application 113017) teach chloromethylation in the presence of Fe.sub.2 O.sub.3 or FeCl.sub.3 as catalyst, regeneration of the chloromethyl methyl ether by reaction with formaldehyde, methanol and HCl, followed by separation of the solvent and aqueous layers from the resin, followed by subsequent separation of the aqueous layer. They then require treatment of the non-aqueous layer containing crude chloromethyl methyl ether with salts which dry the reactant, and thus allow the use of the chloromethyl methyl ether in a second chloromethylation. Reference is made in this patent to East German Unexamined patent application 27643 which was not available to the inventors; according to the present reference, the earlier patent also teaches non-distillative regeneration, but all available references, including an abstract of East German Unexamined patent application 48593, teach such regeneration is accomplished separately from the chloromethylation and after separation of the reacted resin. Further, the process of East German Unexamined patent application 27643 is shown in East German Unexamined patent application 113017 to produce a poor quality of chloromethyl methyl ether, affecting the quality of beads produced after several recyles.
Weber et al, East German Unexamined patent application 236740, teach chloromethylation in the presence of FeCl.sub.3 as catalyst, followed by reaction with methanol, prior to the addition of a stoichiometric amount of paraformaldehyde and HCl gas. The phases are separated but distillation of the newly generated chloromethyl methyl ether is not taught as a means of purifying and recovering the chloromethyl methyl ether; instead, a non-distillative, liquid separation process is taught wherein the FeCl.sub.3, H.sub.2 SO.sub.4, and chloromethyl methyl ether are conducted to the recycle reaction together.
Tada et al, U.S. Pat. No. 4636554, teaches addition of hydrogen chloride in an amount of 0.5 to 10 times (molar) the chloromethyl methyl ether remaining after a conventional chloromethylation reaction, followed by distillation to recover chloromethyl methyl ether. Tada prefers and exemplifies use of solvent; further, Tada regenerates only a portion of the chloromethyl methyl ether necessary to conduct the second chloromethylation. The conditions of Tada will convert some significant portion of the methanol present to methyl chloride (CH.sub.3 Cl), a volatile gas (bp -24.degree. C.) which would be difficult to recover by the distillation techniques employed and would be lost to the environment.
It is an object of the present invention to provide a process for the chloromethylation of aromatic polymeric material which produces chloromethylated product, which proceeds with commercially acceptable yields and reaction times, and which allows repeated preparations to be made without substantial external generation or handling of chloromethyl methyl ether after the initial preparation.
It is a further object to provide a means for efficiently generating chloromethyl methyl ether in a closed reactor, vessel, or container (i.e., one which does not normally require addition of chloromethyl methyl ether from an external source), and efficiently separating said chloromethyl ether, along with the unusual excess chloromethyl methyl ether from the preparation of the chloromethylated resin, from the product. It is a further object to perform such generation of chloromethyl methyl ether without the by-product formation of significant quantities of highly volatile chemicals such as methyl chloride. It is a further object to perform such efficient generation and handling of chloromethyl methyl ether within the confines of the closed apparatus without adversely affecting the structure of the resin being chloromethylated. It is a further object to accomplish the improved process with limited generation of bis(chloromethyl) ether. It is a further object to accomplish the improved process with limited generation of new chloromethyl methyl ether, the amount generated being only that necessary for reaction with the following batch of resin (including a normal excess for fluidization of the reaction product and optionally for swelling the polymer). In the most preferred embodiment, the methanol formaldehyde and HCl are added to the reaction mixture of the chloromethylation reaction when reaction is essentially complete and in an amount stoichiometrically needed to replenish that amount of chloromethyl methyl ether consumed by reaction with the polymer plus and process losses. Additional reactants may be added to help shift equilibrium of the chloromethyl methyl ether decomposition reactions back toward the formation of CME; thus to utilize the decomposition products remaining in the reaction mixture after chloromethylation to recover "regenerated" CME. The principal object of the invention is therefore to, in a single process step, (1) produce new CME ("formation"), (2) recover CME from the reaction mixture ("recycle") and, (3) recover CME from decomposition products ("regenerate"), at least cumulatively sufficient in quantity to conduct the next chloromethylation reaction.